Chromosome Rings in Oenothera, Drosophila and MaizeAuthor(s): Sterling EmersonSource: Proceedings of the National Academy of Sciences of the United States of America,Vol. 18, No. 10 (Oct. 15, 1932), pp. 630-632Published by: National Academy of SciencesStable URL: http://www.jstor.org/stable/85870 .

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630 GENETICS: S. EMERSON PROC. N. A. S.

22 Fettke, C. R., op. cit., 231; Koeberlin, F. R., "The Brewster Iron-Bearing District of New York," Econ. Geol., 4, 737 (1909).

23 Fettke, C. R., op. cit., 234. 24 Schuchert, C., and Longwell, C. R., op. cit., 321-324. 25 Schuchert, C., and Longwell, C. R., op. cit., 321. 26 Emerson, B. K., U. S. G. S. Bull., 597, 48-49 (1917); Emerson, B. K., U. S. G. S.

Mon., 29, 252-299 (1898). 27 White, D.,"Age of the Worcester Phyllite," Wash. Acad. Sci. Jour.; 2, 114-118 (1912). 28 Callaghan, E., "A Contribution to the Structural Geology of Central Massachu-

setts," N. Y. Acad. Sci. Ann., 33, 27-75 (1931). 29 Oral communication of Miss Helen Hoppe.

CHROMOSOME RINGS IN OENOTHERA, DROSOPIILA AND MAIZE

BY STERLING EMERSON

WM. G. KERCKHOFF LABORATORIES OF THE BIOLOGICAL SCIENCES,

CALIFORNIA INSTITUTE OF TECHNOLOGY

Communicated August 17, 1932

In a recent issue of this Journal, Brink and Cooper' have postulated inverted sections in the ring chromosomes of Oenothera to account for the small amount of crossing-over observed in certain hybrids. Their

hypothesis is similar to that previously advanced by Darlington2 which differs chiefly in supposing that there are "differential segments" in the

ring chromosomes instead of inverted sections. Brink and Cooper have further suggested that these inverted sections may be responsible for the more regular disjunction of chromosomes in Oenothera than in maize. The purpose of the present note is to call attention to certain genetic data

already in print which are not in agreement with the interpretations ad- vanced by Darlington and by Brink and Cooper.

In the first place, there is little or no evidence that crossing-over in Oenothera is much less in ring chromosomes than in paired chromosomes. The majority of all linked genes so far studied show very little crossing-over even in paired chromosomes. So far only two linkage groups have been studied extensively: R-v-bu-sp group in chromosome 1-2 and the P-n-s

group in chromosome 3-4. Shull3 has found very little crossing-over between v, bu and sp in his Oe. Lamarckiana crosses in which chromosome 1-2 was presumably a paired chromosome. Sturtevant4 has found little

crossing-over between R and v in crosses in which these genes were known to be in a pairing chromosome. In crosses in which chromosome 3-4 was known to be a paired chromosome, I have recovered no crossovers between s and n in F2 generations5 but have foutnd about 8 per cent crossing-over be-

630 GENETICS: S. EMERSON PROC. N. A. S.

22 Fettke, C. R., op. cit., 231; Koeberlin, F. R., "The Brewster Iron-Bearing District of New York," Econ. Geol., 4, 737 (1909).

23 Fettke, C. R., op. cit., 234. 24 Schuchert, C., and Longwell, C. R., op. cit., 321-324. 25 Schuchert, C., and Longwell, C. R., op. cit., 321. 26 Emerson, B. K., U. S. G. S. Bull., 597, 48-49 (1917); Emerson, B. K., U. S. G. S.

Mon., 29, 252-299 (1898). 27 White, D.,"Age of the Worcester Phyllite," Wash. Acad. Sci. Jour.; 2, 114-118 (1912). 28 Callaghan, E., "A Contribution to the Structural Geology of Central Massachu-

setts," N. Y. Acad. Sci. Ann., 33, 27-75 (1931). 29 Oral communication of Miss Helen Hoppe.

CHROMOSOME RINGS IN OENOTHERA, DROSOPIILA AND MAIZE

BY STERLING EMERSON

WM. G. KERCKHOFF LABORATORIES OF THE BIOLOGICAL SCIENCES,

CALIFORNIA INSTITUTE OF TECHNOLOGY

Communicated August 17, 1932

In a recent issue of this Journal, Brink and Cooper' have postulated inverted sections in the ring chromosomes of Oenothera to account for the small amount of crossing-over observed in certain hybrids. Their

hypothesis is similar to that previously advanced by Darlington2 which differs chiefly in supposing that there are "differential segments" in the

ring chromosomes instead of inverted sections. Brink and Cooper have further suggested that these inverted sections may be responsible for the more regular disjunction of chromosomes in Oenothera than in maize. The purpose of the present note is to call attention to certain genetic data

already in print which are not in agreement with the interpretations ad- vanced by Darlington and by Brink and Cooper.

In the first place, there is little or no evidence that crossing-over in Oenothera is much less in ring chromosomes than in paired chromosomes. The majority of all linked genes so far studied show very little crossing-over even in paired chromosomes. So far only two linkage groups have been studied extensively: R-v-bu-sp group in chromosome 1-2 and the P-n-s

group in chromosome 3-4. Shull3 has found very little crossing-over between v, bu and sp in his Oe. Lamarckiana crosses in which chromosome 1-2 was presumably a paired chromosome. Sturtevant4 has found little

crossing-over between R and v in crosses in which these genes were known to be in a pairing chromosome. In crosses in which chromosome 3-4 was known to be a paired chromosome, I have recovered no crossovers between s and n in F2 generations5 but have foutnd about 8 per cent crossing-over be-

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VOL. 18, 1932 GENETICS: S. EMERSON 631

tween P - :id s (in backcrosses to the double recessive). When chromosome 3-4 was in a ring of 10 (sulfurens. hfranciscana), there was about 5 per cent

crossing-over between P and s,6 wvhich is nearly the same as that observed in pairec chromosomes. The linkage between R and P in fiavens-velans discusse' oy Brink and Cooper involves genes lying in different chromo- somes (1-2 and 3-4) in one of the rings of 4. Perhaps the simplest inter- pretation of the scarcity of crossovers in this case is that both genes lie near the translocation points. Studies on Drosophila show that crossing- over is strongly reduced near the translocation point and a similar reduction is to be expected in Oenothera and in maize. In contrast to the genes already discussed there are two in Oenothera (Co, flower size,7 and br, brevistylis) which give about 50 per cent crossing-over with all other genes regardless of the association of chromosomes in rings. The loci of Co and Br and apparently near the end of one chromosome with about 15 per cent crossing-over between them.4 It can be seen that there is no evidence that crossing-over is reduced in the ring chromosomes of Oenothera, and until there is such evidence it seems hardly necessary to postulate causes of the purely hypothetical reduction.

Darlington2 has assumed that most of fhe genes by which Oenothera complexes differ lie in the mid regions of the chromosomes and that these regions have their homologs not in the adjoining chromosomes but in chromosomes more distant in the ring or in other rings or pairs. (At least that is what I believe Darlington means by "differential segments.") If this were the true condition, then the occasional crossovers which do occur should alter the chromosome configuration in the crossover individual since there would be a new association of ends in the crossover chromo- somes. None of the published cases of crossing-over in rings has given a changed configuration. Among the reported cases are the occasional appearances of sulfur-flowered individuals among the progeny of Oenothera biennis and Oe. suaveolens and of nanella among the progeny of Oe. Lamarck- iana and Oe. biennis. Cleland8 has found that the sulfur-flowered races have the same configurations as their parental forms and Sturtevant9 found that a nanella plant appearing in his culture of Lamarckiana had the same configuration as its sibs. In the crossovers occurring in rings in my cultures4'6 all crossover individuals examined had the same configurations as their immediate parents. From these examples one is justified in con- cluding that most of the genes so far studied do not lie in sections of the chromosomes that are not homologous to corresponding sections in adjoin- ing chromosomes. That such "differential segments" do occur, however, is to be expected in such forms as Oenothera where translocations are so abundant, but such sections could hardly be expected to contain all the genes by which complexes differ as postulated by Darlington.

Brink and Cooper's recourse to inverted sections to account for the

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i.3, GliENI'i'l( '.': S'. MAIEIS'()N - 'r C. N, . S.

regular disjunction of ring chromosomes in Oenotliera is perhaps equally unavailing. Dobzhansky and Sturtevantl? have found that the frequen- cies of the different types of disjunction of ring chromosomes vary from one translocation to another in Drosophila when no inverted sections are

present. Furthermore, unless the inverted sections always involved only the spindle fibre regions, the presence of inverted sections would reduce the Oenothera type of disjunction and cause the chromosomes to be

segregated more nearly at random. It would seem, from our present understanding of Oenothera genetics,

that it is not only unnecessary to postulate inverted section or "differential

segments" in the ring chromosomes to explain certain Oenothera peculiari- ties, but also that such interpretations are not in agreement with the known genetic behavior of this plant.

1 Brink, R. A., and Cooper, D. C., "Chromosome Rings in Maize al( Oenlothera," I'roc. Nat. Acad. Sci., 18, 447-455 (1932).

2 Darlington, C. D., "The Cytological Theory of Inheritance il ()ciothera," Jour.

GeC;et., 24, 405-474 (1931). 3 Shull, G. H., "Crossing-Over in the Third Linkage Group of Oenothera," Proc.

Nat. Acad. Sci., 13, 21-24 (1927); "A New Gene Mutation (mut. bullata) in ()enothera Lamarckiana and Its Linkage Relations," Proc. 5th Internat. Congress of Genetics, Supplementb. Zeitschr. ilndukt. Abst.- Vererbznzgsl., 2, 1322-1342 (1928).

4 Emerson, Sterling, and Sturtevant, A. H., "The Linkage Relations of Certain Genes in Oenothera," Genetics, 17, 393-412 (1932).

5 Emerson, Sterling, "Genetic and Cytological Studies on Oenothera. II," Zeitschr. indJukt. Abst.-Vererbungsl., 59, 382-394 (1931).

'; Emerson, Sterling, "The Inheritance of Certain Characters in Oenothera Hybrids of Different Chromosome Configurations," Geznetics, 16, 325-348 (1931).

7Emerson, Sterling, and Sturtevant, A. H., "Genetic and Cytological Stutdies on O(enothera. III," Zeitschr. indukt. Abst.-Vererbunl.gsl., 59, 395-419 (1931).

x Cleland, R. E., "Meiosis in the Pollen Mother Cells of Oenlothera biennis and Oe. biennis su lfltrea," Genetics, 11, 127-162 (1926); Cleland, R. E. and Oehlkers, F., "Erb- lichkeit und Zytologie verschiedeier Oenotheren und ihrer Kreizeungell," Zahrb. wiss.

Bot., 73, 1-124 (1930). " Sturtevant, A. H., "Genetic and Cytological Studies on Oenothera. I," Zeitschr.

indukt. Abst.- Vererbun gsl., 59, 365-38( (1931). 10 Dobzhansky, T., and Sturtevant, A. H., ''Translocations between the Second

and Third Chromosomes of Drosophila and Their Bearing on Ocnothera Problems," Carnegie Inlst. l1ash., Pub. No. 421, 29-59 (1931).

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